1. Field of the Invention
This invention relates to a microlens substrate, a method for manufacturing the microlens substrate, a liquid crystal panel, and a projection type display apparatus, and more specifically to a microlens substrate for use in an opposed substrate for a liquid crystal panel, a method for manufacturing the microlens substrate, a liquid crystal panel provided with the microlens substrate, and a projection type display apparatus provided with the liquid crystal panel.
2. Description of the Related Art
There is known a projection type display apparatus that projects an image on a screen. In most of such projection type display apparatuses, a liquid crystal panel (liquid crystal light shutter) is normally used for forming the image.
Such a liquid crystal panel has a configuration in which, for example, an opposed substrate for a liquid crystal panel which is provided with a black matrix, a common electrode and the like is joined to a liquid crystal driving substrate (TFT substrate) which is provided with a large number of thin film transistors (TFT) for controlling respective pixels and a large number of pixel electrodes via a liquid crystal layer.
In the liquid crystal panel (TFT liquid crystal panel) having such a configuration, for the purposes of preventing TFT elements from being deteriorated due to light energy of transmitted light and improving contrast of an image, the black matrix is formed in a portion of the opposed substrate for a liquid crystal panel other than the portions thereof that correspond to the respective pixels. For this reason, a region of the liquid crystal panel through which light can transmit is restricted. This makes light transmittance be lowered.
In order to improve the light transmittance for the liquid crystal panel, there is known an opposed substrate for a liquid crystal panel in which a black matrix and/or a common electrode are formed on a microlens substrate provided with a large number of minute microlenses at the positions corresponding to the respective pixels in the opposed substrate for a liquid crystal panel. According to such a liquid crystal panel, light transmitting the opposed substrate for a liquid crystal panel is condensed into openings formed in the black matrix, and this makes it possible to improve light transmittance.
One example of a method of forming such a microlens substrate is disclosed in JP-A 2001-92365. In this method, an uncured photocuring resin material is supplied onto one major surface of a substrate with concave portions in which a plurality of concave portions for forming microlenses are formed. Then, a flat transparent glass substrate is brought into contact with and pressed against the supplied photocuring resin material to thereby cure the supplied photocuring resin material so that the glass substrate is joined to the supplied photocuring resin. Thereafter, the glass substrate is ground and polished so that the glass substrate becomes a cover glass having a predetermined thickness.
However, the method mentioned above requires many manufacturing steps and thus it takes a considerably long time for manufacturing a microlens substrate. Therefore, use of the method gives a large affect to the manufacturing cost of a liquid crystal panel. Further, since a large amount of grinding or polishing particles are generated in the grinding and polishing steps, it is necessary to wash the substrate during and after the grinding and polishing steps. Since such washing is carried out using a large quantity of water, it is not desirable from the viewpoints of natural resource saving and environmental concerns. In addition, there is a case that the photocuring resin material is deteriorated through the washing step, which may result in the case where the product quality of the manufactured opposed substrate for a liquid crystal panel is deteriorated. Further, even in the case where such washing is carried out, there is a possibility that grinding or polishing particles still remain on the manufactured microlens substrate (that is, on the opposed substrate for a liquid crystal panel), so that it is difficult to raise the reliability of the manufactured microlens substrate to a sufficiently high level.
Further, it may be conceived that the grinding and polishing of the glass substrate are omitted. However, this method is not preferable in view of the optical characteristics of the microlens substrate because the thickness of the microlens substrate becomes a considerable thickness. Further, use of such a microlens substrate having the considerable thickness leads to an increased size of a projection type display apparatus.
Furthermore, it may also be conceived that the surface of the glass substrate used for pressing the photocuring resin material is subjected to a releasing mold treatment so that the surface of the cured photocuring resin material is not covered with the glass substrate (cover glass). However, this method involves problems such as follows.
Namely, in general, photocuring resins have poor heat resistance, and therefore there is a case that the constituent material (photocuring resin material) of the microlens substrate is deteriorated due to heat applied when a black matrix and a common electrode are formed on the photocuring resin material constituting the microlens substrate, in particular when they are formed by a chemical vapor deposition method. Further, in general, hardness (shape stability) of photocuring resins even after they have been cured is not so high as compared to inorganic materials, and thus deformation is likely to occur in the cured photocuring resin material when any pressure is applied thereto. This means that if such a photocuring resin material is used as a constituent material of a liquid crystal panel, there is a possibility that any deformation occurs therein. When such deformation occurs, Color Heterogeneity (uneven color distribution) occurs in an image to be displayed by the liquid crystal panel, which results in a lowered image quality of an image to be displayed.